1. Field of Invention
This invention relates to a process for preparing microporous articles. More particularly, this invention relates to a process for the production of microporous polybenzimidazole articles.
2. Prior Art
Microporous products exhibit wide utility in a broad range of separatory fields. For example, microporous fabrics coated with a chemical absorbant can be manufactured into garments that are useful as chemically protective clothing since microporous fabrics possess a larger surface area per unit volume than non-microporous fabrics. See U.S. Pat. No. 4,460,641. In addition, microporous films can be useful as vents, gas-liquid transfer mediums, battery separators and for many other separatory functions. See, for example, U.S. Pat. Nos. 4,460,641, 4,359,510, 3,839,516, 3,801,404, 3,679,538, 3,558,764, and 3,426,754.
To generate such microporous structure, there are a wide variety of known techniques. For example, U.S. Pat. Nos. 4,290,987 and 3,839,516 disclose processes for the preparation of microporous fibers and films by a solvent stretching technique. However, neither of these patents disclose microporous, polybenzimdiazole articles.
U.S. Pat. No. 4,460,641 discloses chemically protective, microporous garments prepared from stretched and heat-set precursor hollow fibers. Although polybenzimidazole polymers are listed as acceptable polymers for the production of the fibers, the process for the preparation of the microporous structure which is disclosed is significantly different from the process of the instant invention.
U.S. Pat. No. 4,336,307 discloses hollow, water absorbing, polyester filaments having fine pores evenly distributed throughout the filaments. The microporous filaments are prepared by melt spinning a blend of a polyester with a sulfonated compound and removing a portion of the sulfonated compound from the filaments by washing it with an aqueous alkali solution. Although the process of this patent has some similarities to the process of the instant applicant, no microporous, polybenzimidazole articles are disclosed.
U.S. Pat. No. 4,055,702 discloses a process for imparting interconnecting microvoids to a solid fiber and impregnating those microvoids with various additives. The microvoids are produced by cold-drawing an undrawn or partially drawn, melt-spun fiber formed from a polyester, polyamide, polypropylene or high density polyethylene polymer in the presence of a nonsolvent, swelling liquid or vapor. See also U.S. Pat. No. 4,530,809 which discloses a similar cold-drawing process along with a hot drawing process. In addition, U.S. Pat. No. 3,325,342 discloses a process wherein a non-crystalline, unoriented, polyamide fiber is treated in an aqueous swelling agent to develop crystallinity and is then drawn to crystalize the yarn. Although processes for the production of microporous structures are disclosed in these patents, neither microporous polybenzimidazole articles nor the specific process of this application are disclosed.
Polybenzimidazoles polymers have been extensively studied recently because of their high degree of thermostability and chemical stability. These polymers have been formed into fibers, films or other shaped articles with great usefulness such as for reverse osmosis, ultrafiltration, ion exchange and electrodialysis separations. See U.S. Pat. Nos. 3,699,038, 3,720,607, 3,737,042, 3,841,492 and 3,851,025.
Although processes for the production of polybenzimidazole polmyer articles of great utility have been disclosed in various patents, none have disclosed the preparation of microporous polybenzimidazole polymers by the disclosed process.
It is therefore an object of the present invention to provide a process for preparing polybenzimidazole articles which are microporous.
It is a further object of the present invention to provide a process for preparing microporous polybenzimidazole articles by means of the addition and subsequent removal of a leachable additive.
It is a further object of this invention to provide a process for the formation of microporous polybenzimidazole articles which are useful in the production of flame retardant materials.
These and other objects as well as the scope, nature and utilization of the process will be apparent from the following description and the appended claims.